feat: add singleton support to World ECS

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/ecs/World.ts

@@ -6,6 +6,7 @@ export class World {
   private nextId: EntityId = 1;
   private components: Map<ComponentName, Map<EntityId, unknown>> = new Map();
   private entities: Set<EntityId> = new Set();
+  private singletons: Map<string, unknown> = new Map();
 
   createEntity(): EntityId {
     const id = this.nextId++;
@@ -48,4 +49,12 @@ export class World {
   getAllEntities(): EntityId[] {
     return [...this.entities];
   }
+
+  setSingleton<T>(name: string, data: T): void {
+    this.singletons.set(name, data);
+  }
+
+  getSingleton<T>(name: string): T | undefined {
+    return this.singletons.get(name) as T | undefined;
+  }
 }

server/src/ecs/__tests__/World.test.ts

@@ -57,4 +57,19 @@ describe('World', () => {
     expect(world.getComponent(entity, 'position')).toBeUndefined();
     expect(world.getComponent(entity, 'needs')).toEqual({ hunger: 100, energy: 100 });
   });
+
+  describe('singletons', () => {
+    it('should store and retrieve singletons', () => {
+      const world = new World();
+      world.setSingleton('testRegistry', new Map([['a', 1]]));
+      const result = world.getSingleton<Map<string, number>>('testRegistry');
+      expect(result).toBeDefined();
+      expect(result!.get('a')).toBe(1);
+    });
+
+    it('should return undefined for missing singletons', () => {
+      const world = new World();
+      expect(world.getSingleton('nonexistent')).toBeUndefined();
+    });
+  });
 });